The present invention relates to means for releasing a screen from a support structure or frame to which the screen is bonded. In particular the invention relates to means for releasing a glass pane or screen (such as a vehicle windscreen) bonded by means of an interposed bonding material to a frame.
Bonded vehicle windscreens commonly need replacing as a result of motoring accidents, vandalism etc. At present, the bonded connection between the windscreen and the support frame is typically released using manual, mechanical means such as the use of sharp angled blades, xe2x80x9ccheese wirexe2x80x9d techniques etc. Use of these known techniques sometimes causes damage to the vehicle (in particular the bodywork and interior trim) which can be expensive to repair. Furthermore, operatives using these known physical techniques are prone to injury as a result of accidents occurring whilst performing the task.
An alternative proposal for an adhesive joint enabling release of a bonded screen from a supporting frame is disclosed in CA-A-2073092 in which a heatable separating member is provided closely fitting or embedded in an adhesive bead. The heatable sealing member disclosed is heated to a temperature at which it is either destroyed or loses adhesion to closely fitting elements or parts of the joint. The disclosure emphasises that the separating element loses its adhesion or is destroyed at a temperature at which the adhesive bead is not damaged.
A problem with the proposal of CA-A-2073092 is that a relatively complex joint is required incorporating discrete heatable element and separate bonding bead which remains substantially unaffected when the heating element is heated. A further drawback is that at present the commercial market for replacement windscreens is substantially restricted to existing vehicles most of which have screens bonded to frames using a single homogeneous bead of polymeric bonding material interposed between the screen and frame. The bonding material is homogeneous to the extent that it is of substantially uniform composition throughout. In this context the homogeneous bonding material may sometimes comprise fillers or other particular additives materials substantially evenly distributed throughout the bonding material.
An improved means of releasing bonded screens has now been devised, which comprises a method of releasing a screen from a frame to which the screen is bonded by interposed homogeneous bonding material, the method comprising the steps of
(a) arranging energy delivery means adjacent the screen; and
(b) transmitting energy from said energy delivery means through material comprising the screen thereby to:
i) cause degradation of material comprising the homogeneous bonding material; and/or
ii) cleavage or degradation of material comprising the screen, thereby to effect release of the screen from the frame.
For performance of the invention in its broadest sense, it is necessary that the screen is transparent to the extent that the energy may be transmitted through the screen to permit release of the screen from the support frame.
The invention is, however, particularly suited for use in releasing (for replacement) vehicle windscreens which are commonly bonded in and to surrounding support frames. In this respect, the screen will typically comprise a material transparent to visible light (such as glass). The homogeneous bonding material preferably comprises a flexible polymeric material (preferably a rubber or elastomeric material such as polyurethane), typically provided as an homogeneous bead extending about the periphery of the screen, interposed between the screen and frame. Such homogeneous bonding material is used in modern vehicle windscreen fitting techniques, almost exclusively.
It is preferred that the mechanism effecting release of the screen from the frame is pyrolytic degradation of the homogeneous bonding material, preferably of a portion of the body of the material most closely adjacent the screen. The degradation of the bonding material may alternatively be by photodissociation or photochemical degradation. Following degradation and release, a remainder portion of the homogeneous bonding material (substantially un-degraded) remains bonded to the frame. Where the bonding material comprises a synthetic organic polymeric material, the degradation when pyrolytic may comprise carbonisation of the material.
The energy delivery means is arranged adjacent a portion of the screen (typically a peripheral portion of the screen) which is bonded to the frame. The energy is then transmitted through the screen toward the location of the bonding material which is interposed between the respective portions of the screen and frame.
It is preferred that the energy delivery means is arranged to deliver wave energy to be transmitted through a localised region of the screen. The wave energy may be electromagnetic wave energy, such as light, or vibrational/sound energy.
In one embodiment, it is preferred that the energy delivery means comprises laser delivery means arranged to transmit laser radiation through the screen to release the screen from the frame. In this embodiment, it is preferred that the laser delivery means is arranged to transmit laser radiation having a wavelength in the visible/near infra-red region of the spectrum. Alternatively, the laser radiation delivered may be in the ultra-violet region of the spectrum.
The laser energy delivery means is preferably directed such that the radiation is transmitted to and absorbed by the bonding material, preferably in a specific portion (or notional layer) most closely adjacent the screen, as described above.
The laser radiation may be focused at a predetermined location. Desirably the laser radiation is continuous wave and enables relatively high intensity/energy radiation to be delivered to, and effect degradation (pyrolytically or otherwise) of, specific localised regions of the bonding material, consequently minimising damage to portions of the screen and un-degraded portions of the bonding material remaining.
Where the energy delivery means comprises ultrasonic delivery means, an ultrasonic transducer is preferably powered to generate ultrasonic energy of sufficient intensity to effect release of the screen. The ultrasonic energy is preferably arranged to be focused (or concentrated) at a predetermined location. The ultrasonic energy may effect release of the screen by pyrolytic degradation of the bonding material and/or cleavage of material comprising the screen. Alternatively, the ultrasonic energy may effect release by other means, such as for example by means of differential induced stresses at the bonding material/screen interface. It is believed that use of ultrasonic energy to effect release of a screen bonded to a frame may be novel and inventive per se.
Whether laser, ultrasonics, or other energy is used, it is preferred that the energy is arranged to be concentrated.
Desirably, the energy delivery means is arranged adjacent a first face of the screen, the screen being bonded to the support structure at a second, obverse, face.
It is preferred that tuning means is provided arranged to tune the frequency or intensity of the wave energy delivered by the energy delivery means.
Typically, the screen comprises glass and may comprise a glass/plastics laminated structure.
The invention is particularly suitable for the release for repair or replacement of vehicle windscreens; it is however suitable for use in other applications, such as for example release of architectural panels or glass screens (windows) bonded to architectural frames.